Polarizing sheets constituted of a polycarbonate have excellent impact resistance and are light, and therefore are used for liquid crystal displays as well as windows of buildings, sunroofs of cars, and sunglasses or goggles to be used for marine sports, winter sports, fishing, etc.
Polarizing sheets, which are obtained by laminating an aromatic polycarbonate sheet as a protection layer through an adhesive layer to each surface of a polarizing film obtained by stretching a polyvinyl alcohol film and staining it with a dichroism pigment (hereinafter arbitrarily referred to as “aromatic polycarbonate polarizing sheet”), particularly have excellent impact resistance and also have high heat resistance, and therefore are used for polarizing lenses for sunglasses or goggles obtained from a curving process or injection molding process.
However, since aromatic polycarbonate has a high photoelastic constant, when a curving process is applied to a spherical or aspherical shape of sunglasses, goggles or the like, a coloring interference stripe tends to easily occur due to retardation. Such a coloring interference stripe has problems such as poor appearance and causing eye strain.
Further, in the case of a polarizing lens obtained by subjecting an aromatic polycarbonate polarizing sheet to a curving process to provide a spherical or aspherical shape, distortion of an image may be caused by unevenness of the thickness of the aromatic polycarbonate polarizing sheet, and there are problems such as poor appearance and causing eye strain.
Regarding retardation caused at the time of applying a curving process, an aromatic polycarbonate polarizing sheet, whose coloring interference stripe has been hidden from view by subjecting an aromatic polycarbonate sheet to be used for a protection layer to a stretching process to cause a large retardation in advance (hereinafter arbitrarily referred to as “stretched polycarbonate polarizing sheet”), is known (Patent Document 1), and is used for polarizing lens products which have excellent appearance and are excellent in saving eye strain.
Meanwhile, a polarizing lens, which is formed by subjecting the afore-mentioned stretched polycarbonate polarizing sheet to a curving process to provide a spherical or aspherical shape, inserting the resultant stretched polycarbonate polarizing sheet into a mold and injecting an aromatic polycarbonate thereto, for the purpose of improving impact resistance more than that of a polarizing lens formed by subjecting the afore-mentioned stretched polycarbonate polarizing sheet to a curving process or forming a corrective lens having a focal refractive power (hereinafter arbitrarily referred to as “aromatic polycarbonate polarizing lens”), is known (Patent Document 2).
In the case of the aromatic polycarbonate polarizing lens, an aromatic polycarbonate is injected and filled in a mold, and therefore, there is an advantage that unevenness of the thickness of the inserted stretched polycarbonate sheet becomes invisible. Therefore, the aromatic polycarbonate polarizing lens is used for lens products without focal refractive power which are particularly excellent in impact resistance, appearance and prevention of eye strain.
In the case of a lens obtained by filling a mold with a thermosetting resin or thermoplastic resin as in the case of the aromatic polycarbonate polarizing lens, the shape of each surface and the thickness of the formed lens can be freely set by suitably setting each surface shape of molds for the lens surfaces and the distance between the surfaces. Therefore, the surface shapes of molds and the distance between the surfaces are set based on the optical design so that the focal refractive power, prism diopter and image distortion of the formed lens become desired values.
In many cases, the surface shape of the formed lens is the same as the surface shape of the mold contacted at the time of forming, but when the surface shape of the lens requires very high precision, in order to compensate decrease of the lens thickness and change of the surface shape due to volume contraction at the time of solidification of the thermosetting resin or thermoplastic resin filled in a mold, the surface shapes of molds for both the surfaces and the distance between the surfaces may be suitably and finely adjusted.
As a mold to be used for the process of curving the aromatic polycarbonate polarizing sheet, a mold having the same shape as the surface shape of a surface opposite to a surface contacting aromatic polycarbonate injected in the aromatic polycarbonate polarizing lens finally obtained is used.
Further, among molds to be used for injection molding of the aromatic polycarbonate polarizing lens, a mold for the stretched polycarbonate polarizing sheet side also has the same shape as the surface shape of the stretched polycarbonate polarizing sheet side in the aromatic polycarbonate polarizing lens finally obtained, and the other mold to be used for injection molding has the same shape as a surface shape by which the focal power and the prism diopter in the aromatic polycarbonate polarizing lens finally obtained based on the optical design can have desired values.
For example, when it is desired to finally obtain an aromatic polycarbonate polarizing lens, which does not have a focal refractive power or prism diopter, and in which the surface of the stretched polycarbonate polarizing sheet side is a spherical surface having a base curve of 8, the curving process may be carried out twice or three times or more. However, the shape of a mold to be used for the final curving process is a spherical surface having a base curve of 8; among molds to be used for injection molding, the shape of a mold for the stretched polycarbonate polarizing sheet side is also a spherical surface having a base curve of 8; and the surface shape of the other mold to be used for injection molding is a spherical surface having a base curve of 8 or slightly greater than 8, wherein the center position of the spherical surface is slightly different with respect to the mold for the stretched polycarbonate polarizing sheet side, that is, decentered.
Further, for example, when it is desired to finally obtain an aromatic polycarbonate polarizing lens, which does not have a focal refractive power or prism diopter, and in which the surface of the stretched polycarbonate polarizing sheet side is an elliptical surface having a base curve in the horizontal direction of 6 and a base curve in the vertical direction of 4, the curving process may be carried out twice or three times or more. However, the shape of a mold to be used for the final process is an elliptical surface having a base curve in the horizontal direction of 6 and a base curve in the vertical direction of 4; among molds to be used for injection molding, the shape of a mold for the stretched polycarbonate polarizing sheet side is also an elliptical surface having a base curve in the horizontal direction of 6 and a base curve in the vertical direction of 4; and the shape of the other mold to be used for injection molding is an elliptical surface having a base curve in the horizontal direction of 6 or slightly greater than 6 and a base curve in the vertical direction of 4 or slightly greater than 4.
Moreover, examples of the surface shape of the aromatic polycarbonate polarizing lens include quadric curved surfaces such as a spherical surface, an elliptical surface and a paraboloidal surface as well as high-order curved surfaces such as a quartic curved surface, and the curvature in the horizontal direction may be different from the curvature in the vertical direction. However, there is a case where the surface shape of the aromatic polycarbonate polarizing lens after injection molding is significantly different from the surface shape of the mold, and the type of difference varies.
Regarding the stretched polycarbonate polarizing sheet, it is known that when forming the aromatic polycarbonate polarizing lens using a mold whose surface shape is a spherical surface, if the stretched polycarbonate polarizing sheet, wherein the stretch of the aromatic polycarbonate sheet at the side where aromatic polycarbonate is injected has been eliminated or decreased, is used, the absolute value of the difference between the base curve in the vertical direction and the base curve in the horizontal direction of the formed polarizing lens (hereinafter arbitrarily referred to as “base curve anisotropy”) is reduced (Patent Document 3).
In the case of the aromatic polycarbonate polarizing lens using the stretched polycarbonate polarizing sheet, wherein the stretch of the aromatic polycarbonate sheet at the side where aromatic polycarbonate is injected has been eliminated or decreased (hereinafter arbitrarily referred to as “one-side stretched polycarbonate polarizing sheet”), the surface shape of the lens can be formed with very high precision. Therefore, the lens is used for products, which are particularly excellent in impact resistance, appearance and prevention of eye strain, and in which precision of the surface shape of the lens is high.
On the surface of the aromatic polycarbonate polarizing lens formed in this way, a hard coating, an antireflection film and the like are suitably formed, and then the lens is fixed to a frame by edging, hole making, screw tightening, etc., thereby providing sunglasses or goggles.